Classification of chemical processes
Globally, all chemical transformations can be divided into three major categories, each with its own unique features.
1. Processes in inanimate nature These occur predominantly in the hydrosphere and atmosphere. Compared to living systems, the diversity of reactions here is small. The main participants are water ($H_2O$), molecular nitrogen ($N_2$), carbon dioxide ($CO_2$), as well as hydrocarbons slowly emerging from the Earth's interior and various volcanic emissions. In an isolated, "pure" form, such processes can be observed only on lifeless planets, such as Mars. On Earth, however, mineral chemistry is inextricably linked with biological chemistry. Even reactions involving oxygen ($O_2$) are driven by life: the main source of this gas is photosynthesis carried out by cells containing chlorophyll.
2. Technological and laboratory processes This is anthropogenic chemistry, planned and implemented by humans. In the natural environment, such reactions practically do not occur. Thanks to this activity, chemistry as a science has been enriched by theories relying on rich experimental material and the synthesis of millions of new substances. However, such technologies have a colossal impact on the environment and billions of people. Mass production of chemical products leads to environmental pollution and the initiation of new, uncontrolled chemical processes that were previously uncharacteristic of our planet.
3. Reactions in living organisms It is in biological systems that the largest number of diverse chemical reactions takes place. The study of the specifics of these cellular transformations is the focus of biochemistry — a science that can figuratively be called "higher chemistry."
Features of cellular chemistry
Chemical processes in cells differ radically from what happens in a researcher's flask or in the atmosphere. They are characterized by the following features:
- Perfect coordination. Reactions do not proceed chaotically; the output yields precisely the amount of products that the cell needs at the given moment.
- Mild conditions. Transformations occur without extreme physical influences (high temperatures or pressures).
- Enzymatic regulation. All processes are controlled by special chemical factors — enzymes. These are highly efficient biological catalysts. Any complex cellular process is serviced by dozens of different enzymes simultaneously.
A classic example of such coordinated work is the replication (doubling) of the DNA molecule in the nucleus, which strictly precedes cell division and ensures the transmission of hereditary information.
Photosynthesis and biomolecular universality
Plants serve as the foundation for sustaining life. During photosynthesis, they absorb solar radiation energy and direct it toward the synthesis of glucose. This process performs a dual function: the organism receives the necessary plastic material and simultaneously stores energy for subsequent life activities.
Subsequently, glucose is transformed into other low-molecular-weight compounds (with the additional involvement of sulfur, phosphorus, and nitrogen compounds). From these simple molecules, the organism assembles complex biopolymers: polysaccharides, polynucleotides, and proteins.
A striking feature of the chemistry of living organisms is its structural economy. Although there are about 100 chemical elements in nature, complex biological macromolecules are built from a very limited, standard set of blocks — peculiar "biological elements." This principle is uniform for all living matter on Earth:
- Proteins are formed from combinations of just 20 universal amino acids.
- DNA is a chain in which only 4 types of nitrogenous heterocycles alternate.
- Fats are synthesized from a glycerol molecule and a limited set (about a dozen) of carboxylic acids.
Briefly: answers to topical questions
Which specific four types of nitrogenous heterocycles alternate in the DNA molecule chain?
The DNA molecule chain alternates four specific types of nitrogenous bases (heterocycles), which are divided into two groups.
- Adenine is a purine nitrogenous base.
- Guanine is a purine nitrogenous base.
- Thymine is a pyrimidine nitrogenous base.
- Cytosine is a pyrimidine nitrogenous base.
These nitrogenous heterocycles pairwise form hydrogen bonds between the two strands according to the principle of complementarity.
What 20 universal amino acids are used to form proteins in the body?
To form proteins in the body, 20 universal proteinogenic L-amino acids are used.
- Glycine (glycine)
- L-alanine (L-alanine)
- L-valine (L-valine)
- L-leucine (L-leucine)
- L-isoleucine (L-isoleucine)
- L-proline (L-proline)
- L-phenylalanine (L-phenylalanine)
- L-tryptophan (L-tryptophan)
- L-methionine (L-methionine)
- L-serine (L-serine)
- L-threonine (L-threonine)
- L-cysteine (L-cysteine)
- L-tyrosine (L-tyrosine)
- L-asparagine (L-asparagine)
- L-glutamine (L-glutamine)
- L-aspartic acid (L-aspartic acid)
- L-glutamic acid (L-glutamic acid)
- L-lysine (L-lysine)
- L-arginine (L-arginine)
- L-histidine (L-histidine)
These amino acids are classified into dispensable, indispensable, and conditionally indispensable.
Which specific enzymes form the complex servicing the DNA replication process?
The complex servicing the DNA replication process includes polymerases and accessory enzymes.
- DNA polymerase — catalyzes the synthesis of the DNA chain; in E. coli, it is the leading enzyme.
- DNA polymerase α — synthesizes the RNA primer to initiate DNA synthesis.
- DNA polymerase δ — catalyzes the synthesis of the leading DNA strand and the elongation of the lagging strand.
- Helicase — unwinds the DNA double helix at the replication fork.
- Topoisomerase — relieves tension ahead of the replication fork.
- RNA primase synthesizes RNA primers to initiate synthesis.
- DNA ligase joins Okazaki fragments on the lagging strand.
- RNase removes RNA primers.
The replication fork also involves SSB proteins, which bind to unwound single-stranded DNA regions and prevent them from re-annealing.
Which carboxylic acids are included in the limited set for the synthesis of natural fats?
The limited set of carboxylic (higher fatty) acids for the synthesis of natural fats includes saturated and unsaturated acids.
- Palmitic acid is saturated.
- Stearic acid is saturated.
- Butyric acid is saturated.
- Myristic acid is saturated.
- Oleic acid is monounsaturated.
- Linoleic acid is polyunsaturated.
- Linolenic acid is unsaturated.
A total of approximately a dozen carboxylic acids are involved in the formation of natural fats.
What structural components make up the monomer of a DNA molecule (nucleotide)?
The DNA monomer (nucleotide) consists of three structural components linked by covalent bonds.
- Nitrogenous base — a purine (adenine, guanine) or pyrimidine (thymine, cytosine) derivative.
- Carbohydrate (pentose) — the five-carbon sugar deoxyribose.
- Phosphoric acid residue — a phosphate group.
The phosphate is attached to the 5'-carbon of deoxyribose, and the nitrogenous base is attached to the 1'-carbon.
To memorize the composition of basic biopolymers, use the «20-4-12» combination: 20 amino acids to build all proteins, 4 heterocycles to encode DNA, and about 12 carboxylic acids to form fats.
Class and exam questions
Where does the bulk of oxygen in abiotic natural reactions come from?
The primary source of molecular oxygen ($O_2$) on Earth is the vital activity of organisms, specifically the process of photosynthesis in plant cells containing chlorophyll.
What are enzymes and why does the cell need them?
Enzymes are highly efficient biological catalysts. They regulate chemical transformations in living organisms, ensuring they proceed under mild conditions and with high precision.
What is the anthropogenic impact on Earth's chemical processes?
Humans have synthesized millions of new substances, leading to uncontrolled reactions in nature. This causes environmental pollution and degradation.
What else to study on this topic
- Mechanisms of enzyme action as biological catalysts
- The process of photosynthesis: from light absorption to glucose synthesis
- Structure and functions of biopolymers (proteins, polysaccharides, polynucleotides)
- DNA replication: chemical aspects of molecular duplication
- Ecological consequences of the mass application of chemical technology products
Master the entire topic in the "Chemistry" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on «Chemistry of Living Organisms» and 3,009 other pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 95 video lessons for the subject
Other topics in "Chapter 18. Major Classes of Bioorganic Compounds"
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.